One of the significant advantageous of a mobile terminal, such as a mobile telephone, a portable digital system (PDA), a pager, a laptop computer or other portable electronic device, is the mobility afforded the user. In this regard, a mobile terminal is able to move freely throughout a network and between networks while continuing to communicate via the network(s). Typically, a mobile terminal is capable of transmitting signals to and for receiving signals from base stations. A base station is, in turn, a part of one or more cellular or mobile networks that each include additional elements required to operate a network, such as a mobile switching center. In operation, the mobile switching center is capable of routing calls to and from the terminal via one or more base stations when the terminal is making and receiving calls. The mobile switching center can also provide a connection to landline trunks when the mobile terminal is involved in a call.
The signals transmitted between the base station and a mobile terminal may be encrypted. In a Code Division Multiple Access (CDMA) system, for example, the messages that are transmitted via the air interface, such as between a base station and a mobile terminal, are encrypted by means of an encryption key. As described by the 3rd Generation Partnership Project 2 “3GPP2” specification 3GPP2 C.S0005-C, Version 1.0, entitled Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems, Release C (May 28, 2002), the encryption key may be a Cellular Message Encryption Algorithm (CMEA) key generated using the cellular authentication and voice encryption (CAVE) algorithm in networks supporting 2G wireless communications protocols or an (IK, CK) key pair as a result of Authorization and Key Agreement (AKA) in networks supporting 3G wireless communications protocols.
A network is generally divided into a plurality of areas that are individually identified by means of a system identification number (SID) and a network identification number (NID). In this context, a system is a wireless communication service that covers a geographic area such as a city, metropolitan region, county, group of counties or the like and is uniquely identified by a SID, while a network is a subset of a system that may be as large or small as desired so long as the network is contained in one system and is uniquely identified within a system by a NID. For example, a network may be all base stations controlled by a respective base station controller.
For those base stations within a particular area identified by a respective SID/NID, the signals transmitted between the base stations and a mobile terminal are encrypted with a respective encryption key. The encryption key is only utilized within the particular area, however, such that movement of the mobile terminal to another area identified by another SID/NID will require signals transmitted between the mobile terminal and the base stations of the other area to be encrypted by means of another encryption key. Thus, the communications between a mobile terminal and the base stations within each area are encrypted by means of unique encryption key.
Upon initiation of communication between a base station and a mobile terminal within a respective area, the base station and the mobile terminal perform a registration and/or authentication process which, among other functions, establishes an encryption key to be utilized for subsequent signals transmitted between the base stations and the mobile terminal within the respective area. In the registration and/or authentication process, the mobile terminal generates an encryption key, while the base station generally obtains a corresponding encryption key from a respective visitor location register (VLR) or authorization center within the system. In a CDMA system, for example, the mobile terminal and the base station establish appropriate encryption keys by means of either an SSD update procedure or an authentication key agreement procedure. The mobile terminal and the base stations in the network identified by the respective SID/NID thereafter exchange signals encrypted with the encryption keys. As the mobile terminal moves from one area to another area as identified by a change in the SID/NID, the mobile terminal must repeatedly engage in the registration and/or authentication process with the base stations within each different area so as to establish the encryption keys to be utilized for subsequent communications within that area.
As will be recognized, the registration and/or authentication process by which encryption keys are established for subsequent communication within a respective area require significant network resources and slow the onset of actual communication with the mobile terminal pending establishment of the encryption keys. These disadvantages are multiplied in instances in which the mobile terminal crosses back and forth over the boundary between adjoining areas. In this situation, the entire registration process generally need not be repeated, but a resynchronization registration process or other type of authentication process must be repeatedly performed to establish the encryption keys. In particular, the mobile terminal may maintain a list of areas by SID/NID within which the mobile terminal has recently conducted communications. As such, upon the return to an area within which the mobile terminal had previous communication, the mobile terminal will recognize that the mobile terminal was recently registered with the base stations in the area and therefore need not repeat the entire registration process. However, the mobile terminal will conduct a resynchronization registration process or other type of authentication process with the base stations in the area, typically in response to receipt by the base station(s) of a signal from the mobile terminal that cannot be decrypted. Among other things, this resynchronization registration process establishes the encryption keys utilized during a subsequent communication session within the area. As noted above, this resynchronization registration or other type of authentication process must be repeatedly conducted upon entry of the mobile terminal into a different area to obtain the encryption key utilized for communications within that area even though the mobile terminal may have recently been within that same area and communicated in an encrypted manner with the base stations within that area in accordance with the same encryption key, thereby disadvantageously consuming system resources to reestablish the encryption key and delaying the onset of communications pending reestablishment of the encryption key.